The present invention concerns a microdialysis probe and catheter arrangement including a probe to be inserted in the body of a living being in order to perform various analyses.
Microdialysis is used to monitor the interstitial fluid and blood in various body organs with respect to local metabolic changes. The technique involves sampling the chemistry of blood or body fluids of by analyzing the perfusate of a microdialysis probe inserted into a blood vessel, or, a tissue, respectively.
Microdialysis has been used both in experimental set-ups and in clinical situations, preferably for studies of brain metabolism. By introducing a microdialysis catheter into a blood vessel or a tissue, the content of the perfusate reflects the composition of the blood or the body fluid, respectively, over time due to the diffusion of substances back and forth over the dialysis membrane.
Relevant background art includes U.S. Pat. Nos. 4,694,832; 5,106,365; 6,264,627; and 6,346,090.
U.S. Pat. No. 4,694,832 to Ungerstedt discloses a dialysis probe comprising a dialysis membrane with associated ducts for achieving a perfusion fluid flow over the membrane. The single membrane is tubular and consists of a thin-walled permeable hose material referred to as a xe2x80x9chollow fiberxe2x80x9d membrane. Ducts are provided for supplying and removing perfusion liquid to and from the interior of the membrane, and one of these ducts is disposed inside the hollow fiber membrane to extend to the distal end thereof. In order to protect and support the very thin membrane, the membrane is surrounded by a mounting, which is more rigid than the membrane and is preferably made as a thin-walled metal sleeve. The membrane is inserted in the mounting to be as close as possible to the wall of the sleeve. The wall of the sleeve has an opening in which a portion of the membrane surface is exposed.
U.S. Pat. No. 5,106,365 discloses a microdialysis probe comprising an outer sleeve containing tubes for delivering and removing dialysis products. The dialysis membrane is directly fixed to the end edge of the outer sleeve by gluing.
U.S. Pat. No. 6,264,627 by the present inventors concerns a catheter comprising an elongate catheter body, having a distal end and a proximal end. An outer essentially cylindrical surface, limiting a wall structure, encloses at least two channels including a first and a second channel for microdialysis solution. Each channel has a proximal end and a distal end. The first and second channels are interconnected at a first distance from the distal end of the catheter body so that microdialysis solution can flow from one channel to the other. An opening is provided in the catheter body at a second distance from its distal end, and a microdialysis membrane is arranged to cover the opening. A space in the catheter body formed by a portion of the first channel in connection with the opening forms a microdialysis chamber, having at least a portion of the microdialysis membrane as a part of its walls. The proximal ends of the first and second channels are connectable to external means for circulating, monitoring and/or analyzing the dialysis solution.
U.S. Pat. No. 6,346,090, also by the present inventors, discloses a microdialysis catheter comprising an elongate catheter body having first channel means for delivery of dialysis liquid and second channel means for discharge of dialysis liquid. A portion of the catheter body has a reduced diameter forming a straight cylindrical portion. A relatively stiff supporting sleeve is arranged around the cylindrical portion. A plurality of tubular membrane members is arranged in close relation to one another in one layer about the outer circumference of the supporting sleeve. Each tubular membrane member has an inlet end and an outlet end embedded in annular blocks arranged about the cylindrical portion at a proximal and a distal end thereof, respectively. The blocks allow fluid communication between the first channel means and one of the inlet and outlet ends of the plurality of tubular membrane members, and allow fluid communication between the second channel means and the other of the inlet and outlet ends of the plurality of tubular membrane members.
In microdialysis, the recovery, i.e., the percentage of specific substances obtained in the perfusate as compared to the true value in the surrounding blood or tissue, depends on various factors. The most important factors are the size of the pores in the membrane, the number of pores, the area of dialysis membrane, the perfusate volume in the dialysis chamber and the perfusion rate. To obtain a maximum recovery of substances from the blood or body fluid, it is desirable that the membrane area is as large as possible and that the rate and volume of perfusate contained in the dialysis chamber are as low as possible.
However, in order to achieve an acceptable time lag of 10-15 minutes or less with a low perfusion rate and good recovery, the catheters can have only a limited length, and that is the situation today.
It would be desirable, however, to enable the use of longer catheters, but this is not practicable due to the resulting extended time lags.
It is a problem, thus, to combine a low flow rate in the dialysis chamber in order to obtain good samples with a short transportation time for the samples from the dialysis chamber to the proximal end of an outlet channel.
It is an object of the present invention to solve the problem of providing a catheter having a high flow rate as regards return flow from a dialysis chamber, while still maintaining a low flow rate in the dialysis chamber to enable a proper diffusion over the dialysis membrane.
According to the present invention there is provided a probe and catheter arrangement, said catheter comprising an elongate catheter body having at least three internal channels extending therealong, a first of said channels delivering dialysis liquid to a dialysis chamber and a second of said channels discharging dialysis liquid from said dialysis chamber, a third of said channels communicating with said second channel to deliver a second liquid to said second channel to increase the flow rate therein.